• 한국재료학회지
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• 제15권6호
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• pp.393-398
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• 2005

The crystal structure and magnetic properties of the $Mg_{1-x}Zn_xFeAlO_4\;(0{\leq}x\leq1.0)$ have been investigated by means of x-ray diffractometry and $M\ddot{o}ssbauer$ spectroscopy. The samples$(0{\leq}x\leq1.0)$ have been prepared by the ceramic sintering method. The x-ray diffraction pattern shows that the crystal structure of the samples is a cubic spinel type. The lattice constant has been found by extrapolation using the Nelson-Riley function and it increases slightly from $8.3496\AA\;to\;8.4128\AA$ with Zn concentration. The $M\ddot{o}ssbauer$ spectra for x<0.4 show a superposition of two sextets ana a paramagnetic doublet at room temperature. The superparamagnetic doublet for x<0.4 seems to be due to Al ion in tetrahedral site by the superparamagnetic clustering effect.

• 한국재료학회지
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• 제11권10호
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• pp.859-862
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• 2001

The crystal structure and magnetic properties of the $Ni_{1-x} Cd_xFeAlO_4$(0$\leq$x$\leq$0.5) have been investigated by means of X-ray diffractometry and Mossbauer spectroscopy. The samples($0\leq$x$\leq$0.5) have been prepared by the ceramic sintering method. The X-ray diffraction pattern shows that the crystal structure of the samples is a cubic spinel type. The lattice constant has been found by extrapolation using the Nelson- Riley function and it increases slightly from $8.321{\AA}$ to $8.410{\AA}$ with Cd concentration. The Mossbauer spectra for x<0.4 show a superposition of two sextets and a paramagnetic doublet at room temperature. The cation distribution for x=0 was determined to be $[Fe_{0.75}Al_{0.25}]^A[NiFe_{0.25}Al_{0.75}^BO_4$. The superparamagnetic doublet for x< 0.4 seems to be due to A1 ion in tetrahedral site by the superparamagnetic clustering effect.

• 한국항공운항학회지
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• 제14권2호
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• pp.17-26
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• 2006

The flutter characteristics of all movable tail wing with honeycomb sandwich structure have been studied in this study. The present wing model has a airfoil cross section and the linear variation of spanwise thickness. Structural vibration analysis is performed based on the finite element method using sandwich and beam elements. Unsteady aerodynamic technique used on the doublet lattice method has been effectively used to conduct the frequency-domain flutter analyses. The parametric flutter studies have been performed for various structural design parameters. Computational results on flutter stability due to the variation of structural parameters are presented and its related characteristics are investigated through the comparison of results.

• Journal of Magnetics
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• 제18권1호
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• pp.21-25
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• 2013

Nickel substituted manganese ferrites, $Mn_{1-x}Ni_xFe_2O_4$ ($0.0{\leq}x{\leq}0.6$), were fabricated by sol-gel method. The effects of sintering and substitution on their crystallographic and magnetic properties were studied. X-ray diffractometry of $Mn_{0.6}Ni_{0.4}Fe_2O_4$ ferrite sintered above 523 K indicated a spinel structure; particles increased in size with hotter sintering. The M$\ddot{o}$ssbauer spectrum of this ferrite sintered at 523 K could be fitted as a single quadrupole doublet, indicative of a superparamagnetic phase. Sintering at 573 K led to spectrum fitted as the superposition of two Zeeman sextets and a single quadrupole doublet, indicating both ferrimagnetic and paramagnetic phase. Sintering at 673 K and at 773 K led to spectra fitted as two Zeeman sextets due to a ferrimagnetic phase. The saturation magnetization and the coercivity of $Mn_{0.6}Ni_{0.4}Fe_2O_4$ ferrite sintered at 773 K were 53.05 emu/g and 142.08 Oe. In $Mn_{1-x}Ni_xFe_2O_4$ ($0.0{\leq}x{\leq}0.6$) ferrites, sintering of any composition at 773 K led to a single spinel structure. Increased Ni substitution decreased the ferrites' lattice constants and increased their particle sizes. The M$\ddot{o}$ssbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and the octahedral sites of the $Fe^{3+}$ ions. The variations of saturation magnetization and coercivity with changing Ni content could be explained using the changes of particle size.

• 한국재료학회지
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• 제9권8호
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• pp.854-857
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• 1999

Fe-Se-Te계(FeSe(sub)1-xTe(sub)x, x=0.2, 0.5, 0.8)의 특성을 X-선 회절법 및 Mossbauer 분광법에 의해 조사하였다. 결정구조는 세 시료 모두 주된 tetragonal PbO 구조와 hexagonal NiAs 구조가 일부 혼합된 형태를 보였으며 x=0.5의 경우 tetragonal 구조의 격자상수 값은 a=3.795$\AA$, c=5.896$\AA$ 이며 c/a=1.55로 나타났다. 다양한 온도변화에 의해 측정된 Mossbauer 스펙트럼은 전체 시료 모두 초미세 자기구조를 갖지 않는 강한 이중선(doublet)이 관측되었다. 조성 및 온도변화에 대해 뚜렷한 선형(line shape)의 변화는 관측되지 않았으나 결합상태에 약간의 변화를 보였다. 이성질체 이동(isomer shift)값과 사중극자 분열(quadrupole splitting)값 및 온도의존성을 분석한 결과 Fe는 low spin이 +2가 상태로 존재하며 강한 공유 결합상태임을 알 수 있었다. x=0.8의 경우 이성질체 이동값의 온도변화는 제2차 도플러 효과(second order Doppler effect)의 영향인 것으로 나타났다.

• 한국자기학회지
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• 제17권1호
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• pp.18-21
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• 2007

Pulsed laser deposition(PLD) 박막 증착법을 이용하여 hexagonal $HoMn_{1-x}-Fe_xO_3$(x=0.0, 0.05) 물질을 박막으로 $Pt/Ti/SiO_2/Si$ 기판 위에 증착하였다. 또한 x-ray diffraction(XRD), atomic force microscopy(AFM), scanning electron microscope(SEM), 및 x-ray photoelectron spectroscopy(XPS)를 통하여 박막의 결정학적 및 미세 구조를 분석하였고, conversion electron $M\"{o}ssbauer$ spectroscopy(CEMS)를 이용하여 자기적 특성에 관해 연구하였다. 결정구조는 hexagonal 구조로써 space group이 $P6_3cm$로 분석되었고, single crystal과는 달리 (110) 방향으로 우선 배향성을 가지고 증착되었다. $HoMn_{0.95}Fe_{0.05}O_3$ 박막의 경우 single crystal과 비교했을 때 hexagonal unit cell의 $c_0$ 축은 일정하나 $a_0$ 축은 다소 감소함으로 분석되었다. 이는 박막 증착에 사용된 $Pt/Ti/SiO_2/Si$ 기판과의 lattice mismatch 때문으로 해석된다. Fe가 미량 치환된 $HoMn_{0.95}Fe_{0.05}O_3$ 박막을 상온에서 CEMS 측정을 수행한 결과, $HoMn_{0.95}^{57}Fe_{0.05}O_3$ 분말의 경우 magnetic $T_N$이 72K 부근이므로, 상온에서 doublet absorption spectrum이 관측되었고, 전기사중극자 분열값(quadrupole splitting; ${\Delta}E_Q$)이 $1.62{\pm}0.01mm/s$로 비교적 큰 값을 가짐을 확인하였다.

• 항공우주기술
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• 제6권1호
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• pp.35-44
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• 2007

본 연구에서는 선미익을 채용한 경항공기인 반디호의 수출형 시제기에 대한 플러터 해석을 수행하였다. 내부 하중 생성용 유한요소모델을 기초로 강성 모델을 작성하였고, 중량 통제를 위한 중량 DB에 근거하여 중량 모델을 작성하였다. 공력모델은 DLM을 이용하였다. 작성된 모델을 이용하여 1차 플러터 해석을 수행하였다. 이를 토대로 주요 진동 모드를 구분해 내고, 지상진동시험을 수행하여 진동 특성을 획득하였다. 획득된 고유진동수를 근거로 유한요소모델의 수정이 이루어졌고 2차 해석이 수행되었다. 해석 결과 주요 플러터 근의 특성을 정리하였다. 가장 중요한 플러터 근은 롤 운동을 갖는 강체 모드와 반대칭 주익 피칭 모드의 연계 모드로 판명되었다.

• Journal of Magnetics
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• 제15권1호
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• pp.25-28
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• 2010

This study examined the crystallographic and magnetic properties of vanadium-substituted lithium cobalt titanium ferrite, $Li_{0.7}Co_{0.2}Ti_{0.2}V_{0.2}Fe_{1.7}O_4$. Ferrite was synthesized using a conventional ceramic method. The samples annealed below $1040^{\circ}C$ showed X-ray diffraction peaks for spinel and other phases. However, the sample annealed above $1040^{\circ}C$ showed a single spinel phase. The lattice constant of the sample was $8.351\;{\AA}$, which was relatively unaffected by vanadium-substitution. The average grain size after vanadium-substitution was $13.90\;{\mu}m$, as determined by scanning electron microscopy. The M$\ddot{o}$ssbauer spectrum could be fitted to two Zeeman sextets, which is the typical spinel ferrite spectra of $Fe^{3+}$ with A and B sites, and one doublet. From the absorption area ratio of the M$\ddot{o}$ssbauer spectrum, the cation distribution was found to be ($Co_{0.2}V_{0.2}Fe_{0.6})[Li_{0.7}Ti_{0.2}Fe_{1.1}]O_4$. Vibrating sample magnetometry revealed a saturation magnetization and coercivity of 36.9 emu/g and 88.6 Oe, respectively, which were decreased by vanadium-substitution.

• Journal of Magnetics
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• 제21권3호
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• pp.308-314
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• 2016

Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, $MnFe_2O_4$, $Mn_{0.8}Co_{0.2}Fe_2O_4$, $Mn_{0.8}Zn_{0.2}Fe_2O_4$ and $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The $MnFe_2O_4$ ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The $M{\ddot{o}}ssbauer$ spectrum of the $MnFe_2O_4$ ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the $M{\ddot{o}}ssbauer$ spectra of the $MnFe_2O_4$, $Mn_{0.8}Co_{0.2}Fe_2O_4$, and $Mn_{0.8}Zn_{0.2}Fe_2O_4$ ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. However, the $M{\ddot{o}}ssbauer$ spectrum of the $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$ ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the $M{\ddot{o}}ssbauer$ spectra could be used to determine the cation distribution equation, and we also explained the variation in the $M{\ddot{o}}ssbauer$ parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure $MnFe_2O_4$, the saturation magnetizations and coercivities were larger in $Mn_{0.8}Co_{0.2}Fe_2O_4$ and smaller in $Mn_{0.8}Zn_{0.2}Fe_2O_4$, and $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.

• Journal of Magnetics
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• 제15권4호
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• pp.159-164
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• 2010

The Zn, Co and Ni substituted manganese ferrite powders, $Mn_{1-x}$(Zn, Co, Ni)$_xFe_2O_4$, were fabricated by the solgel method, and their crystallographic and magnetic properties were studied. The Zn substituted manganese ferrite, $Zn_{0.2}Mn_{0.8}Fe_2O_4$, had a single spinel structure above $400^{\circ}C$, and the size of the particles of the ferrite powder increased when the annealing temperature was increased. Above $500^{\circ}C$, all the $Mn_{1-x}$(Zn, Co, Ni)$_xFe_2O_4$ ferrite had a single spinel structure and the lattice constants decreased with an increasing substitution of Zn, Co, and Ni in $Mn_{1-x}$(Zn, Co, Ni)$_xFe_2O_4$. The Mossbauer spectra of $Mn_{1-x}Zn_xFe_2O_4$ (0.0$\leq$x$\leq$0.4) could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. For x = 0.6 and 0.8 they showed two Zeeman sextets and a single quadrupole doublet, which indicated they were ferrimagnetic and paramagnetic. And for x = 1.0 spectrum showed a doublet due to a paramagnetic phase. For the Co and Ni substituted manganese ferrite powders, all the Mossbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. The variation of the Mossbauer parameters are also discussed with substituted Zn, Co and Ni ions. The increment of the saturation magnetization up to x = 0.6 in $Mn_{1-x}Co_xFe_2O_4$ could be qualitatively explained using the site distribution and the spin magnetic moment of substituted ions. The saturation magnetization and coercivity of the $Mn_{1-x}$(Zn, Co, Ni)$_xFe_2O_4$ (x = 0.4) ferrite powders were also compared with pure $MnFe_2O_4$.